The hydrogenation effect on the Er luminescence at 1.54 mum in an Er-doped amorphous Si quantum dot film was investigated. After hydrogenation, the luminescent properties were different between large-dot (2.5 nm) and small-dot (1.4 nm) samples. In particular, the number of optically active Er ions was increased in a large-dot sample, but decreased in a small-dot sample. We propose that the hydrogenation causes the Er migration toward an Si dot, and the luminescent property depending on the dot size is originated from the number of Er ions near an Si dot before hydrogenation. (C) 2005 The Electrochemical Society.